In a resent information-oriented society, movable digital assistants, particularly, personal digital assistants (PDA) have been the center of public attention. One of the objectives to be achieved by the personal digital assistants is a lowering of power consumption. As the display device for use in the personal digital assistants, a liquid crystal display device has been most commonly used. There is also great demand for a lowering of power consumption in respect of the liquid crystal display device.
The liquid crystal display devices are roughly classified into two types, namely, passive matrix type and active matrix type. The active matrix type liquid crystal display devices are superior to the passive matrix type liquid crystal display devices in terms of the display quality. One type of the active matrix display device uses a three-terminal non-linear element, such as a TFT (thin film transistor), as a switching element. Another type of the active matrix display device uses a two-terminal non-linear element, such as an MIM (metal insulator metal), as a switching element. The two-terminal type switching element has the following advantages over the three-terminal type element. Namely, the two-terminal type switching element can be obtained at low cost because it can be produced by a simple process. Moreover, since there are only two terminals, the electrode wiring is simpler, and therefore the two-terminal type switching element achieves a higher aperture ratio of the pixel.
The active matrix type liquid crystal display devices using the two-terminal non-linear element can achieve high-contrast and even displays by an amplitude selective addressing scheme, but suffers from a drawback that a residual image (seizure) is apt to occur. In order to reduce the residual image, for example, an addressing scheme disclosed in Japanese publication of unexamined patent application (Tokukaihei) No. 8-262406 employs a method of switching one selecting period of a scanning signal among three voltage levels (the driving method with the selection period being divided into the first through third periods).
Here, a conventional driving method of this type is explained. First, referring to FIG. 3, a typical structure of a liquid crystal display device is explained.
The liquid crystal display device includes a liquid crystal display panel 50. The liquid crystal display panel 50 is provided with data electrode lines X1 through Xn, and scanning electrode lines Y1 through Ym. Additionally, in order to drive the liquid crystal panel, the liquid crystal display device includes a control section 55 for generating control signals, voltage generating circuits 51, 53 for generating voltages according to the control signal, a scanning electrode driver 54 for generating a scanning signal based on the voltage generated by the voltage generating circuit 53 and applying the scanning signal to the scanning electrode lines Y1 through Ym, and a data electrode driver 52 for generating a data signal based on the voltage generated by the voltage generating circuit 51 and applying the data signal to the data electrode lines X1 through Xn.
Referring now to FIG. 16, the following description will explain various signals used in the driving method with the selection period being divided into the first through third periods. In FIG. 16, V.sub.P represents a scanning signal applied to the scanning electrode lines Y1 through Ym. The scanning signal V.sub.P is generated as follows.
The voltage generating circuit 53 generates scanning electrode driver input signals V.sub.H, V.sub.L, V.sub.M, and inputs these signals into the scanning electrode driver 54. Here, the scanning electrode driver input signal V.sub.H is a rectangular wave in which voltages V.sub.1 and V.sub.2 alternately appear, and the scanning electrode driver input signal V.sub.L is a rectangular wave in which voltages V.sub.4 and V.sub.5 alternately appear. The scanning electrode driver input signal V.sub.M is a constant voltage as a non-selected voltage.
In the scanning electrode driver 54, the scanning voltage V.sub.P is generated based on the scanning electrode driver input signals V.sub.H, V.sub.L, V.sub.M according to control signals such as a scanning clock signal LP, a scanning start signal S and an alternating inverted signal M. Specifically, the scanning electrode driver 54 generates the scanning voltage V.sub.P by selectively outputting the scanning electrode driver input signal V.sub.H or V.sub.L in a selecting period T.sub.S, and by outputting the scanning electrode driver input signal V.sub.M as the non-selected voltage in a non-selecting period.
In order to generate a rectangular wave by outputting voltages of two different levels alternately like the scanning electrode driver input signal V.sub.H or V.sub.L, the voltage generating circuit 53 includes a voltage switching circuit shown in, for example, FIG. 17. The voltage switching circuit shown in FIG. 17 has a p-channel MOS transistor 151 and an n-channel MOS transistor 152 so as to generate the scanning electrode driver input signal V.sub.H. By controlling the p-channel MOS transistor 151 and n-channel MOS transistor 152 to be repeatedly turned into the ON state and OFF state alternately by control signals CS1, CS2, input voltages V.sub.1, V.sub.2 are alternately output as an output voltage V.sub.0. As a result, the scanning electrode driver input signal V.sub.H is generated.
FIG. 18 is a waveform illustration showing the relationship between the output voltage V.sub.0 of the voltage switching circuit of FIG. 15 and an output current I.sub.0. When a voltage like the output voltage V.sub.0 is applied to a capacitive element, such as a liquid crystal, a reverse current a is produced as shown by the waveform of the current I.sub.0 in a switching timing from the high voltage V.sub.2 to low voltage V.sub.1. The reverse current a is a cause of a waste of power, and increases the power consumption. Furthermore, this voltage switching circuit requires an input voltage of the same level as an output voltage. Therefore, the peripheral members that perform voltage switching need to have a withstand voltage not lower than the output level, resulting in an increase in the production cost.